The present invention relates to container closures, and more particularly to closures having threads formed thereon and related methods.
Conventional injection molded, plastic closures often include a circular top member, a cylindrical skirt that depends downwardly from the top member, threads formed on the interior of the skirt, and a tamper evident band formed on a lower rim of the skirt. Typically, such closures are molded in a one-step process such that the top member, skirt, and threads are integrally formed. Closures having threads integrally molded as part of the skirt typically require a rotary capper operation to twist the threaded closure onto matching threads on the container finish. A conventional rotary capper process is relatively slow and requires expensive machinery compared with commercial, high-speed, conventional press-on or in-line capper technology.
Conventional composite closures typically include a metal panel for covering and sealing to a container rim and a threaded plastic band for coupling to mating container threads. U.S. Pat. No. 5,685,443 discloses embodiments of such a band that may be pressed-on and twisted-off.
Another type of conventional closure is formed of an integral metal top member and metal skirt. A particular type of metal skirt is formed with a smooth, cylindrical sidewall. A liquid or flowable material, such as plastisol, is subsequently applied to the skirt inner wall, usually by spraying while the closure is spinning. The plastisol, or like material, is formed on the skirt sidewall by a process that includes baking, curing, or a similar treatment step. U.S. Pat. No. 5,190,177 discloses a press-on, twist-off metal closure having a conventional lining into which threads are formed by the container thread, and requires a baking or curing step.
Further, the baking or curing process makes it difficult or infeasible to provide such a metal closure with an integrally formed, frangible tamper evident band of the type that depends from the bottom of the skirt and detaches upon removal of the closure from the container. Although the metal top member may include a button-type tamper evident feature, for hot-fill applications, it is often preferable to employ a frangible, tamper evident band. For example, the U.S. Pat. No. 5,190,177 discloses that the tamper evident band is formed by a separate security ring that is fitted into an annular shoulder formed on the peripheral skirt.
Thus, there is a need for improved closures, and techniques for forming closures.